Biomech
6/4/99

•	When born 88% water
•	When elderly, 70% water
•	Change in collagen and proteoglycans is important as we age
•	When young, type II collagen
•	Slightly acidic environment
•	Cells of the disc fxn in anaerobic conditions
•	Over life span, the disc increases 10% in width and height
•	Discs do not normally shrink, if it does, there’s some pathological component
•	Technically, shouldn’t shrink w/age if anything shouldn’t get taller
•	Females shrink more than men, due to collapsing of endplates (fish vertebrae)
•	What is creep and how does it affect the disc?
•	Taller in the morning than when you go to bed
•	Disc has time to rehydrate over the night
•	Shrink like a ¼” during the day by noon
•	Normal aging does not affect the disc
•	Vibration—hysteresis affect—loss of energy every time load and unload, over time have a harder time getting back to its normal shape
•	Over time becomes inflamed and brings water back into the disc, hyper-pressure not as elastic (w/stands pressure from above), not able to move as much, loss of ROM
•	Derangement
•	0—no injury
•	1—small—no pain
•	2—medium—no pain
•	3—break—pain—why would the nucleus want to flow into the annulus—it won’t unless turn the solid into a liquid
•	disc is largest avascular structure
•	immunological—foreign material esp the nucleus which acts like an antigen to the body, blood vessels enter the area and start immune response to nucleus—last trimester
•	still see large inflammation response—cells from the nucleus bring the inflammation upon itself
•	leads to liquefying the disc and it will exit through a pre-existing tear in the annular fibers
•	larger disc bulge w/no pain tends to reabsorb itself
•	smaller disc bulge w/pain remains—nucleus is solid and is just pushing on the annular fibers

•	endplate fractures—schroml nodes—very common, typically not pain
•	valsalva, SLR, Well Leg Raise—95% chance that it is a disc bulge
•	lumbar spine ½ is L4 and other ½ is L5
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